Field of the Invention
The present invention concerns a method for planning a magnetic resonance imaging examination of an examination subject that contains an implant, as well as a planning computer for planning such an examination, and a magnetic resonance apparatus and a non-transitory, computer-readable data storage medium for implementing such a method.
Description of the Prior Art
In a magnetic resonance (MR) apparatus, also referred to as a magnetic resonance tomography system, the body of an examination object to be examined, for example a patient, a healthy test subject, an animal or a phantom, is exposed with a basic field magnet system to a relatively high basic magnetic field, for example of 1.5 or 3 or 7 Tesla. In addition, gradient fields are applied with the use of a gradient coil arrangement. Radio-frequency (RF) pulses (excitation pulses), are then radiated by suitable antenna devices via a radio-frequency antenna unit, which leads to the nuclear spin of specific atoms resonantly excited by these radio-frequency pulses being flipped by a defined flip angle in relation to the magnetic field lines of the basic magnetic field. During the relaxation of the nuclear spin, radio frequency signals, so-called magnetic resonance signals, are emitted, which are received by suitable receive antennas and are then further processed. Finally, the desired image data can be reconstructed from the raw data thus acquired.
A specific magnetic resonance sequence, also called a pulse sequence, is activated in order to operate the data acquisition scanner of the MR apparatus for a specific measurement. The pulse sequence is a sequence of radio-frequency pulses, for example excitation pulses and refocusing pulses, as well as gradient pulses to be activated coordinated thereto on different gradient axes in different spatial directions. Readout windows are set, adapted to the aforementioned pulses in time, which predetermine the periods of time in which the induced magnetic resonance signals are acquired.
Magnetic resonance imaging may be implemented for an examination object in whose body an implant is situated. This can be a passive implant, such as an artificial knee joint, an artificial hip, a breast implant, a dental implant, a surgical fixing implant, a clip, an artificial heart valve, or a stent, for instance. It is also possible for an active implant to be located in the examination object, such as a heart pacemaker, a defibrillator, an implant for deep brain simulation (brain pacemaker), a cochlear implant, or a vagus nerve stimulator. Other implants known to those skilled in the art can of course also be situated in the body of the examination object.
The gradient fields or radio-frequency fields created while magnetic resonance imaging is being carried out can be problematic in relation to such an implant in the examination object. For example for a heating of the implant or a malfunction of an active implant to occur during magnetic resonance imaging. Guaranteeing the safety of the examination object and the integrity of the implant located in the examination object during magnetic resonance imaging are therefore of great significance.